RESPIRATORY and swallowing movements are activities that have been noted in utero. In fact, it is not unusual to detect a fetus sucking their thumb as early as four months before birth. At birth, the infant exhibits two reflexes related to sucking. The root reflex, which lasts until the child is approximately seven months old, is the movement of an infant’s head and tongue towards a stimulus touching the infant’s cheek.

The sucking reflex—the active movement of the infant’s muscles surrounding the mouth—expresses milk from the nipple and lasts for approximately 12 months. To obtain milk from the mother’s breast, the infant does not need to suck but instead stimulates the smooth muscle in the breast to contract and express milk onto the tongue. This is called suckling. The milk is carried to the throat and gullet by the tongue. The infantile swallow does not occur in the same way as it does in adults. It is characterised by the infant placing their tongue beneath the nipple, contracting the lower lip, and swallowing with the lips together and jaws apart.

From a medical perspective, it is not unusual for a child to suck a finger or, sometimes, even a pacifier until the age of 30 months. However, if the habit persists beyond that age, the damage done to the oral structures may require corrective procedures.

In fact, when a child over the age of three habitually sucks their fingers, it can give rise to 12 different harmful effects, which may lead to disfigurement of the entire dentition, upper and lower jaws, lips, and palate. The consequences—depending on the frequency, intensity, and duration of the habit—almost always result in an alteration of the child’s natural facial features.

The term adenoid facies has been used to describe the facial appearance of patients with a long face and anterior open bite. This condition often stems from habitual mouth breathing. More specifically, these patients demonstrate a downward and backward rotation of their lower jaw during growth, excessive eruption of posterior teeth, upper jaw constriction, anterior open bite, and increased anterior (especially lower) facial length.

We must remember that the main functions of the oral cavity are respiration, swallowing, mastication, and speech. The ultimate shape of the lips and jaws may not be determined by genetics alone but also by habitual behaviour. Newborn infants are obligatory nasal breathers, but the mandible (lower jaw) and tongue must be positioned away from the throat for the airway to remain open. If nasal breathing becomes obstructed, oral breathing must commence, which can lead to complications. Respiratory needs, therefore, can be a primary determinant of lower jaw posture and tongue position in later years.

A multitude of factors influences the early growth and development of the facial region. Habits can affect the orofacial structures and influence facial growth, oral function, occlusal (bite) relationships, and facial aesthetics. In other words, a child may even grow up not resembling their parents due to certain deleterious habits formed during their early years.

On the other hand, the adult swallow is characterised by a tooth-together swallow, with the tongue against the palate and lips relaxed. The transition from the infantile way of sucking to the adult way is gradual, and disruption of this normal process can result in abnormal physical changes in the middle and lower sections of the face.

The instances in which harmful habits during childhood can modify a person’s facial appearance are too numerous to mention here. However, the advice given is that professional intervention should be sought whenever a young child is observed practising abnormal oral habits.